Secondary trunking system



Nov. 3, 1925.

J.- l. BELLAMY ET AL SECONDARY TRUNKING SYSTEM 4 Sheets I Filed May 17, 1923 InUEzn UI'E Juhn I.EE:ZZsm.1; Juhn E- Eardns:

Nov. 3, 1925. v 1,559,736

J. l. BELLAMY ET AL.

SECONDARY TRUNKING SYSTEM J h I E 22 fi fi f 'un. 5am%, an EII'Z'IEI' Patented Nov. 3, 1925. V

UNITED STATES 1,559,736 PATENT OFFICE.

J OEZN' I. BELLAM'Y, OF CHICAGO, ILLINOIS, AND JOHN E. GARDNER, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOBS '10 AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

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Application filed May 17, 1823. Serial No. 639,518.

To all whom it may concern:-

Be it known that we; Joan I. BELLAMY- and JOHN E. GARDNER, citizens of the United States and Oanada,.respectively,residents of Chicago, Cook County, and State of Illinois,

and Wilkinsburg, Allegheny County, and

State of Pennsylvania, respectively, have jointly invented certain new and useful Improvements in Secondary Trunking Systoms, of which the following is a spec1fication. 7

The present invention relates in general to secondary trunking systems of the type used principally in automatic and semi-automatic telephone systems, but is concerned more particularly with such systems of the above named character as are used to provide increased trunking efliciency between a group of automatic selectors on a certain level and the succeeding group of switches, although the invention is by no means limited thereto; and the principal object, briefly stated, is the production of a new and improved secondary trunking system using finder switches that are preselecting, that is, set on the next trunks to be used before such trunks are taken for use.

Another object of the invention which is incidental to the carrying out of the main object is the production of suitable circuit arrangements whereby each primary trunk in the improved trunking system is rendered non-selectable to the selector switches having access to it until a finder switch has actually selected that trunk.

Another object is the production of suitable circuit arrangements whereby ,a suitable number of trunks in each primary subgroup are preselected to take care of the calls as they 'come in.

The other objects have to do mainly with the details of carrying out of the invention and can, therefore, be best understood from the detailed description to be given subsequently.

Referring now to the drawings comprising Figs. 1-4, inclusive, they show by means:

of the usual circuit diagrams a sufiicient amount of apparatus in a system embodying the principles of the invention to enable the same to be understood.

Figure 1 is a trunking diagram and shows the scheme used in cross-connecting between a main group of 250 primary trunks coming from selector switches on a particular level of the banks thereof and the banks of 150 finder switches of the preselecting type. Itis assumed that there are 25 primary subgroupsof'iten trunks each, the sub-groups 4-24, inclusive, being omitted in order to avoid an unnecessary complication of the drawingsb Since there" are ten trunks in each primary sub-group, and since there must be at least one trunk. from each primary sub-group to each secondary subgroup, the maxlmum number of sub-groups into which the secondary group of trunks can be divided is ten. The secondary trunks are shown divided into this maximum number of sub-groups and one trunk in each sub- 1 group is shown. These trunks are represented by the finders F inclusive. It is assumed that the finders used are of the single motion type and that each has access to 25 primary trunks, of which only four are shown. I v

It will be noted that the cross-connecting on the intermediate distributing frame IDF is such that the trunks in each ofthe succeeding primary sub-groups after the first primary sub-group PSG are slipped one trunk as regards the connection of the trunks of the preceding primary sub-group. For example, the first trunk in the first primary sub-group PSG is cross-connected to the first secondary sub-group, the second trunk to the second secondary sub-group, the third trunk to the third secondary subgroup, etc., while the first trunk in the second prima sub-group PSGr is cross-connected tot e second secondary sub-group instead of the first, the second trunk to the third secondary sub-group, etc., to the tenth trunk which is cross-connected to the first secondary sub-group.

Referring now to Fig. 2, this drawing shows the selector D which is assumed to be a selector having access on one level to the ten trunks in the primary sub-grou PSG Fig. 1. Of these trunks, only the rst and tenth, T. and-T 9, .are shown.

Figure 13 shows the trunk circuits TC I and T0 through which the trunks T and T respectively, pass before they reach the asis shown in Fig. 1. Figure 3 shows also the finders F and F which, together with the other finders in their respective secondary groups, have access to the trunks TC and TC, respectively. The repeaters R and R are associated with the finders F and F respectively, owing to the fact that the associated trunks are outgoing trunks extending to another oflice in the system.

Figure 4 shows the connection of the starting circuits to the sub-group of finders in which the finder F is located. ()n the lefthand side of the drawing, the twenty-five incoming starting circuits SC SC inclusive, are shown, and are extended through the contacts of the chain relay 169 to the fifteen finders numbered F F inclusive. This drawing will be explained more in detail hereinafter.

The selector D, Fig. 2, is mechanically of the well-known vertical and rotary type, of which the bank contacts are arranged in horizontal rows or levels.

The finder F Fig. 3, is mechanically of the well-known rotary type of switch of which the wipers have no normal position and move in a forward direction only. The remaining finders, such as the finder F are identical with the finder F The repeater R which is associated with the finder F through the medium of the three conductors 166-468, inclusive, is provided primarily to permit the use of a twoconductor trunk instead of a three-conductor trunk extending to the next ofiice. The other repeaters of the system, such as the repeater R are similar to the repeater R The system has been described in general, and in order to give a better understanding of the same, a detailed description of the operation of the system will now be given. For this purpose it will be assumedthat the primary sub-group PSGr is being put into operation for the first time; that the remaining part. of the finder system is already in operation; that the trunks of this sub-group are wired complete; and that the battery supply has just been completed to them. That being the case, a circuit is closed for the starting relay 101, Fig. 3, as follows:

From ground by way of the uppermost armature of relay 105 and its resting contact, similar armatures and contaetsin the intervening trunk circuits, armature 113 of relay 110 and its resting contact, and the marginally adjusted starting relay 101to battery. Upon energizing, relay 101 disconnects ground from the common conductor 104, thereby removing the ground potential from test contact 139 in the bank of the finder F and also from the test contacts of the other trunks in the same primary subgroup. As a further result of the energization of relay 101, it places groundon start conductor 130 at armature 102. This ground potential is extended by Way of armature 114 and its resting contact, armature 119 and its resting contact, conductor 131, jumper 136 on the frame IDF, armature 170 and its resting contact of chain relay 169, armature 159 and its resting contact, and line relay 154 of the finder F to battery. Upon energizing over the above traced circuit, relay 154 opens a. point in the extension of the start circuit at armature 163; closes a circuit for switching relav 153 and stepping magnet 151 in series at armature 162; and at armature 161 connects test wiper 142 to the junction of switching relay 153 and stepping magnet 151.

The further operation of the finder F 'depends upon whether the trunk upon which the wipers 141-143, inclusive, are standing, is a trunk of a primary sub-group in which two trunks are preselected or is a trunk of a primary sub-group in which two trunks are not preselected (it has been decided to show a system in which two trunks are maintained preselected). In the latter case, the test contact upon which test wiper 142 is resting is ungrounded, the operation of armature 161 of relay 154 is ineffective, and switching relay 153 energizes immediately in series with stepping magnet 151.

Assuming, however, that the trunk upon which the wipers of the switch are standing is associated with a primary sub-group in which two trunks are already preselected, test wiper 142' engages a grounded test contact; switching relay 153 is short-circuited;

and the Wipers of the finder are rotated step by step in search of an ungrounded test con tact by the buzzer-like action of stepping magnet 151 which is operated through test wiper 142 and which interrupts its own circuit at the interrupter contacts 152. When test wiper 142 reaches an ungrounded test contact, which contact it will be assumed is the test contact 139, stepping magnet 151 does not energize again owing to the absence of ground potential on test contact 139,

and switching relay 153, being no longer short-circuited, energizes in series with stepping magnet 151. Stepping magnet 151, however, does not energize at this time on account of the high resistance of switching relay 153. Upon energizing, switching relay 153 closes a point in the circuit of chain relay 169 at armature 156; opens the circuit of line relay 154 and extends the start conductor 164 to the resting contact of the operated armature 163 of the line relay at armature 159; disconnects test wiper 142 from the junction of switching relay 153 and stepping magnet 151 at armature 158, there by preparing the holding circuit of switching relay 153; and at armatures 155 and 160 connects up the line Wipers 141 and 143. In

response to line wiper 141 being connected up, relay 110 in the trunk circuit TC eneri armature 155 and its workin gizes over the following circuit: From ground by way of the high resistance relay 110, armature 118 and its resting contact, jumper 133, bank contact 138, wiper 141,

contact, conductor 166. upper left winding of the repeating coil associated with the repeater R, and the upper winding of line relay 171 to battery. Vhile the high resistance relay 110 energizes over this circuit, relay 171 of the repeater B does not energize at this time on account of the high resistance of relay 110. Upon energizing, relay 110 removes the ground potential from the release trunk conductor 68 of the associated trunk T at" armature 117, thereby rendering this trunk accessible to the selector D and the other switches in whose banks this trunk is multipied; prepares a circuit for relay 111 atarmature 116; and at armature 115 disconnects test contact 139 from the normally grounded conductor 104 and connects it to ground, thereby closing a holding circuit for switching relay 153 of the finder F before the slow-acting line relay 154 has had time to ance 112 at armature 113, thereby placing in the trunk circuit TC, and at armature 163 extends the start conductor 164 to the start conductor 165 of the next finder in the same secondary sub-group.

The trunk T is now preselected and rendered accessible. to the selector D.

The next trunk in order is preselected by a finder inthe second secondary sub-group, Fig. 1, such as, for example, the finder F. lVhen this occurs, another resistance, such as 112,. is placed in series with the marginally adjusted relay 101, whereupon said relay 101 decnergizes; replaces ground on the common conductor 104 at armature 103, thereby rendering the remaining eight trunks in this sub-group inaccessible to the finders by grounding the test contacts of said trunks; and at armature 102 removes ground from the starting circuit.

vits interrupter contacts 42 again.

vertical magnet 40 at armature 53 and at armature 52 places ground on release trunk conductor 28, thereby establishing a holding circuit for such preceding switches as may be included in the connection.

When the calling subscriber operates his callin device in accordance with the next digit in the desired number, the circuit of line relay 35 is opened a corresponding number of times. Each time line relay 35 deenergizes in response to one of the interruptions thereby produced, it closes a circuit for vertical magnet 40 as follows: From ground by way of the resting contact of armature 59 and said armature, armature 51 and its resting contact, armature 53 and its working contact, relay 37, and vertical magnet 40 to battery. By the operation of vertical magnet 40, the wipers 61-63, inclusive, are raised opposite the desired level of bank contacts. Relay 37 is energized in series with vertical magnet 40 and, being slow-acting, retains its armature attracted throughout the vertical movement. As a result of the energization of relay 37, it closes a circuit at armature 54 for stepping relay 38 by way of off normal contacts 43 (which close upon the first verticalstep) and interrupter contacts 42. Stepping relay 38, upon energizing, closes a locking circuit for itself 1 at armature 55, and at armature 56 prepares a circuit for rotary magnet 41.

At the end of the vertical movement, slow acting relay 37 deenergizes and completes the circuit of rotary magnet 41 at armature 54. Rotary magnet 41, upon energizing, advances the wipers 61,63, inclusive, into ongagement with the first set of bank contacts in the selected level, and, nearthe end of its stroke, opens the circuit of stepping relay 38 at interrupter contacts 42. Stepping relay 38, upon deenergizing, opens the circuit of rotary magnet 41 at armature 56, whereupon rotary magnet 41 deenergizes also and closes the trunk T terminating in the first ,set of bank contacts is still idle, switching relay 39 energizes immediately. Assuming for the moment, however, that the trunk is busy, switching relay 39 is short-circuited by the ground potentialencountered by test wiper 62, and stepping relay 38 energizes from this same ground potential and closes the circuit of rotary magnet 41 again, whereupon the switch wipers are rotated into engagement with the next set of bank contacts. This 211 In case ternate operation of stepping relay 38 and rotary magnet 41 continues until an idle" trunk is reached, whereupon switching relay when switching relay 39 energizes in series with. stepping relay'38 at the end of the first rotary step. Stepping relay 38, however, does not energize at this time on accountof the high resistance oft switching relay 39. 39, upon energizing, re-

Switching rela moves ground rom armature 51 of line relay 35 at armature 59, thereby opening the circuit of release relay 36, and at armature 58 disconnects test wiper 62 from the junction of switching relay 39 and stepping relay 38 and connects it to the grounded re lease trunk conductor 28, thereby placing ground on test contact 65. This ground potential extends through test contact 65, release .trunk conductor 68, and armature 116 and its working contact to relay 111. Relay 111, upon energizing, disconnects release trunk conductor 68 from armature 117 and places a shunt around armature 11.6 and its working contact at armature 122; extends release trunk conductor 68 to the release trunk conductor 167 of the repeater R at armature 121; disconnects test contact 139 from conductor 104 at still another point by means of armature 120; shifts the auxiliary from'the windings of line relay 35 and ex tend them by way of wipers 61 and 63, bank contacts 64 and 66, conductors 67 and 69, jumpers 133 and 135, Fig. 3, bank contacts 138 and 140, wipers 141 and 143, armatures 155 and 160 and their working contacts, conductors 166 and 168, and the left-hand windings of the repeating coil of the repeater R to the upper and lower windings of line re lay 171. Line relay 171 now energizes vover conductors 27 and 29 and closes a circuitfor release relay 172 at armature 173. Release relay 17 2, upon energizing, places ground on release trunk conductor 167, thereby closing a holding circuit for relay 153 of, thefinder F relay 111 of'the trunk circuitTC, switching relay 39 of the selector 1), and the similar relays of the preceding switches.

As a further result of the energization'of line relay 171 of the repeater R a bridge is closed across the outgoing trunk conductors 166 and 167 at armature 174, whereupon .energization ofzrelay 110 willv now be deing subscriber operates his calling device in the automatic switchin the distant-office to I Y which" this outgoing 'tru-nk'i'extends is pre- I pared for operation, in the usual m'annen The efiect of the previously-mentioned described. When relay 110" deenergizes"in response to being disconnected at "armature 118, it places' a. shunt 'aroundfres'istance' 112, leavin onlyone such resistance in the circuit 0% relay 1.01; When this occurs, relay 101 energizes, again ',disconnects ground from conductor 104 at armature 103; and

places ground on the .start' conductor at armature 102, whereupon the thir'dtrunk T Fig.1, is preselected in the usual manner by a finder in the third secondarysub group, such as, for example the finder Ffl' Fig. '1.

Returning now, to the call which-islb'eing" traced through the system, when thelxcallaccordance' withv the subsequent digit or 6 digits in the desired number,"l'ine-relay'171 is deenergized in accordance with the man ips .ulations ofthecalling device in; the usual manner and, 1 upon each deen'ergization, opens the bridge across'conductors 176 and 177 at armature 174, thereby causing the connection to be extended 'to the desired line in the distant ofiice in the well-known manner. y v

' When the calling subscriberreplaces] his receiver either after having com leted the connection or having abandone the call, line relay 171 deenergizes and opens the circuit of release relay 172 andalso thebridg e across the conductors of; the 'interoflice trunk at armature 174. The switches in the distant oflice are released in the usual man ner. Release relay 172, upon'deenergizing in response to the prolonged opening of its m circuit, removes ground from ,"release conductor 167 at arma'tur'e--175,- whereupon switching relays 39 and '153.Iof;.the selector D and the finder F respectively, deener gize as well as the holding relay 111 of the trunk circuit TCF. The deenergization of relays 111 and 153 restoreconditions in the associated circuits to normal, and the deenergiza'tion of switching relay 39 offthe selector Dfresults in a circuit being closed for release magnet 44 at armature 59. This circuit, includesfarmature 51 an'dit-s resting contact, armature 53 and itsrestingcohtact.

randfoff 'normal contacts 45. The wipers of" the selectorJD are restoredto normal position in theusual' manner .in response to the energlzatlonof release magnet 44 and the circuit of said :release magnet 44] is opened at off'normal contacts 45bythe; switch shaft when thewipers reach their-normal position. 5

Itwill be notedithat upon the deenergization of holding-relay111 of the trunk .circu'it TC the trunk T is again made busy to the switches having access to it by the f ground potential which is placed on conduca,

"ing circuit can possibly be tor 68 at armature 122 and its resting congization of start relay 101, a finder in the first secondary sub-group will be started to again preselect the trunk T It will be noted that conductor 165, which is the start conductor outgoing from the finder F is dotted for a ways and'then returns to the incoming start conductor 164 of the finder F This arrangement represents the well-known loop starting circuit and the dotted portion of conductor 165 indicates the contacts in the other finders in the same secondary sub-group. This startappreciated more fully upon reference being had to Fig. 4, which represents how the twenty-five starting circuits SC SC inclusive, of which one is provided for each trunk accessible to a finder, are distributed to the fifteen finders in the first secondary sub-group. The starting circuit SC can be found on Figs. 3 and 4 both, as well asth'e armatures 159 and 163 of the relays 153 and 154 of the finder F Also, the conductors 164 and 165 can be located in both drawings. It is thought that the above will be suflicient to enable the starting circuit to be understood, in view of the fact that such starting circuits are well-known. The novel part of this arrangement resides in the method of switching the starting circuits by means of the chain relay 169., This chain relay is energized when all of the associated finders are busy and disconnects all the starting c1rcuits from the finders and extends each back over its own'conductor to its own trunkcircuit. This enables a finder to be started, in case one is available, even though the secondary sub-group to which the start wire of the trunk next in order extends happens to be busy. For example, in case the trunk T Fig.3, is idle-and it becomes necessary to preselect another trunk in this primary sub-group, starting relay 101 energizes as described hereinbefore and places ground on the start conductor 130. This ground potential extends over the previously traced circuit to armature 170 and, assuming that the first secondary sub-group is busy and that chain relay 169 is consequently energized,

the ground potential is extended through armature 170 and its working contact to 1 conductor 132-by way of the IDF jumper 137. This results in the next idle trunk T or T for example, being preselected instead of the primary sub-group being handit of the fact that it is imp ossible at this time to preselect' the trunk In case it so hap ensthat the start relay 101 energizes in or er to effect the preselection of another. trunk, and that all the non-- preselected trunks are busy, or that none of the non-preselected trunks are available for preselection, either due to being busy or due to the fact that one or more of the associated secondary sub-groups are busy, the starting ground is extended to the meter M which operates to register such a condition. There is a meter such as M associated with each of the primary sub-groups and the'number of operations of one of these meters within a given time is'a'fair indication of the number of times when trunks are needed when they are not available; The number of operations of the meter M, however, is not an indication of the number of times that all .the

trunks in that particular primary sub-group are actually busy, or unavailable because the associated secondary sub-groups are busy, on account of the fact that this meter operates when one trunk is actually preselected and idle in the primary sub-grou and another call must come in to this sub-group after this condition exists before the last available trunk is taken.

From the foregoing description it is seen that the resent invention makes it possible to secure an efiicient group of outgoing secondary trunks with the addition of a minimum amount of switching equipment, namely finders, and Without introduclng extra trunk hunting time between the calling of successive digits in a number, owing to the fact that the trunks are preselected and that the only trunk hunting time involved in any particular case is the time required for a selector, such as the selector D, to operate to select a preselected trunk.

- "We claim:

1. In a telephone s stem, primary trunks,

secondary trunks, a nder switch associated with each secondary trunk, primary switches having access to said primary-trunks, means for causing part of said finder switches to select primary trunks ahead of calls, and means for rendering selectable to said primary switches only such primary trunks as have been selected by said finders.

- 2. In a telephone svstem, primary trunks secondary trunks, a finder switch associated with each secondary trunk, primary switches having access to said primar trunks, said primary trunks being norma ly non-selectable to said primary switches, means for causing certain ones of said primary trunks to be selected by said finders, andv means for rendering the selected primary trunks selectable to said primary switches.

finder banks and so arranged that the finder switches in each group have access to at least one trunk accessible to each group of selec tors.

4.'In a telephone trunking system, a plurality of groups of selector sw tches, a plurality of groups of finder switches, banks for said finder switches multipled within each group/but not between groups, and trunk lines connecting the selector banks with the finder banks and so arranged that each of said selector switches has access by the same primary movement to at least one trunk accessible to each finder.

5. In a telephone system, a plurality of groups of selector switches, each having directive vertical and automatic rotary movements, a plurality of groups of finder switches having automatic rotary movement only, and trunk lines extending from corresponding levels of the banks of all said groupsof selectors to the banks of said finders, said trunk lines being so arranged that .difierent groups.

7. In a telephone system, a plurality of groups of finder switches, a plurality of grou s of trunks terminating in the banks of said finders at one end, groups of switches for connecting the. said trunks at the other end with calling lines, therebeing a separate grou of switches assigned to each group of tru s and a distributing frame on which the said trunks are so arranged that the trunks associated with an particular roup.

of switches terminate in nders in di erent groups.

8. In a telephone trunking system, means for connecting calling and called lines comprising selector switches of the type which restore to normal after each connection and finder switches of the type which do not restore to normal after each connection trunk lines extending from-thebanks' of said selectors tothe banks of the said finders, and means for insurin that any operated selector will always se ect a trunk line which is already engaged by an idle finder.

9. In a telephone trunking system, means I- a group of finder switches having access to for connecting a callin and a called line comprising a selector switch, a trunk line accessthle to said:-'-;selector, a second trunk line, and fia finder j'srvitch individual to said second trunk line and having access to said first trunk line, all said switches and trunk lines being connected together in serial relation upon'the establishment of the connection, and means for restoring the selector to normal when the callin party hangs up while the said finder is maintained in selective position with regard to said first trunk.

10. In a telephone trunking system, a group of selectors, groups of finders, trunk lines extending from the banks of said selec' tors to the banks of said finders, means for maintaining some idle one of said finders in engagement with one of said trunk lines, and means for preventing any operated selector from connecting with one of said trunk lines which is not engaged by an idle finder. i

11. In a telephone trunking system, selector switches, finder switches, trunk lines connecting the selector banks with the finder banks, means for causing the finders to preselect trunk lines ahead of the calls, and means for causing the selectors to select the trunks which have been preselected by the finders.

12. In a telephone system, selector switches, finder switches, trunk lines connecting the selector banks with the finder banks, means for causing a certain number of said finders to preselect trunk lines ahead of the calls, means for causing subsequently operated selectors to select the preselected trunks, and means for causing other of said finders to preselect other of said trunks as fast as those already preselected are taken for use.

13. In a telephone trunking system, trunk lines finder switches having access to saidv and means for preventing said devices .from

connecting calling lines with any trunk lines that are not preselected.

-14.-In a telephone system, a group of trunk lines, a group of lines, primary switches for connecting an one of said lines with any one of said trun lines at one end thereof, a second group of trunk lines, secondary switches for connecting any trunk line in the first group with any trunk line in the second group of trunk lines, means for preselecting a trunk line of the first group for use and means responsive to the preselection 0t such trunk line for operating one of said secondary switches to connect such trunk line with a trunk line in the second group.

15. In a telephone system, two trunk lines,

the first trunk line and notto the second trunk line, a second group of finder switches having access to the second trunk line and not to the first trunk line, a start conductor for starting said finders extending to the first of said trunk lines, a branch start conductor normally connected to said, start conductor at one end and extending to the first group of finders, a normally ooen branch of said start conductor extending from the first trunk to the second trunk and from thence through a normally connected branch to thefirst trunk line.

16. In a telephone system, two trunk lines, a group of finder switches having access to the first trunk line and not to the second trunk line, a second group of finder switches having access to the second trunk line and not to the first trunk line, a start conductor for starting said finders extending to the first trunk line, a branch start conductor normally connected to said start conductor at one end and extending to the first group of finders, a normally open branch of said start conductor extending 'from the first trunk to the second trunk and from thence through a normally connected branch to the second group of finders, a return conductor connected to said normally open branch at one end and extending to the first finder group, and a relay operated responsive to the-condition of all finders busy in the first group to disconnect the associated branch of the start conductor from such group of finders and to connect it instead to said return conductor.

17. In a telephone system, a group of finder switches, an incoming start wire nor-' mally connected to said group, an outgoing start wire, and a relay operated responsive to the condition of all finders busy within the'group to disconnect said incoming start wire from the group and to connect it insteadto said outgoing start wire.

I l8. In a telephone system, a group of finder switches, a plurality of start conductors incoming to said finder switches, a like plurality of start conductors outgoing from said finder switches, and a relay 0 erated responsive to the condition of all sai finder switches being busy to disconnect said incoming start conductors from said finder switches and to connect them instead to said outgoing start conductors.

19. In a telephone system, a plurality of trunk lines, a like plurality 0 groups of finder switches associated with said trunk lines, respectively, the finder switches in each grou having access to the associated trunk line ut not to any of the other ones of said trunklines, a start conductor extending to the first of said trunk lines,- means individual to said trunk line for extending said conductor from the first trunk line to the second trunk line, and other means individual to the associated group 'of finder switches and operative responsive'to a busy condition existing in the finder group for extending said start conductor from the first trunk to the second trunk.

20. In a telephone system, a group of trunk lines, finder switches having access to said' trunk lines, other lines, switching mechanisms for connecting said other lines with said trunk lines, means for causing said trunk lines to be preselected by said finder switches, and means responsive to the said trunk lines for rendering 'the first namedmeans ineflt'ective.

21. In a telephone system, a group of trunk lines, finder switches having access to said trunk lines, other lines, switching mechanisms for connecting said other lines preselection of a predetermined number of with said trunk lines, means for causing said trunk lines to be preselected by said finder switches, means responsive to' the preselection. of a predetermined number of said trunk lines for rendering the first named means ineffective, and means responsive to' the connecting of a predetermined number of said trunk lines with a like number of'.

7 ductors of the finder switches are connected,

and jumpers connecting the contacts on the two sides of the frame so as to connect all the conductorsof each trunk line with the proper conductors in any desired group of finder switches.

23. In a telephone trunking system for connecting calling and called lines, primary and secondary trunk lines, automatic hunt- I ing switches, means for operating said switches ahead of the calls to connect idle primary and secondary trunk lines together in airs, ndrmally open sets of contacts in eac of the talking conductors extending through each of said switches, and means in each switch for closing the associated sets of contacts whenever the switch is in use for connecting trunk lines as set forth.

24. In a telephone system, two groups of lines, a group of trunk lines associated with the first group of lines, a second group of trunk lines associated with the second group of lines, a group of switching devices effective to connect any one of the lines in the first group with any one of the associated trunk lines, but ineffective to connect any one of said lines in the first group with any one of the trunk lines associated with the lines in the second group, and inflective also to connect any one of the trunk lines associated with the lines of the first group with any one of the lines of the second group, a;

group of switching devices effective to connect any line in the second group with any one of the associated trunks, but ineffective to connect any line in the second group with any one of the trunk lines associated with the first group, and ineffective also to connect any one of the trunk lines associated with the second group with any one of the lines of the first group, a plurality of groups of finder switches, multiple connections between the bank contacts of each finder and the other finders in the same group but not group of trunks, a distributing frame on which the said trunks are so arranged that the trunks associated with any particular group of switches terminate in finders in different groups, and relays connected in said trunks between said groups of switches and the distributing frame for controlling the operation of said finder switches.

26.. In a telephone system, a plurality of groups of primary trunks, a plurality of groups of secondary trunks, a like plurality of groups of secondary switches for connecting primary and secondary trunks together, groups of switches for connecting the said primary trunks at the other end with calling lines, there being a separate group of such switches assigned to each group of primary trunks, a distributing frame on which the said primary trunks are so arranged that the primary trunks in .any particular primary group terminate at different secondary groups of switches, and relays connected in said primary trunks on the primary trunk side of. the distributing frame for controlling said secondary switches. y

In witness whereof, I hereunto subscribe 'my name this 9th day of May A. D. 1923.

JOHN I. BELLAMY. In witness whereof, I hereunto subscribe my name this 10th day of May, A. D. 1923.

. JOHN E. GARDNER. 

